Documenting forest juvenilization in high-elevation old-growth forests in southern inland British Columbia, with implications for the winter ecology of Canada’s endangered Deep-Snow Caribou

Climate change is altering high-elevation conifer forests in western North America, with potential impacts on species dependent on these ecosystems. We investigated recent, locally widespread tree mortality patterns in old-growth Engelmann spruce–subalpine fir forests in southern British Columbia, with special reference to the winter foraging needs of Canada’s endangered Deep-Snow Caribou (DSC), tied almost exclusively to heavy loading of arboreal hair lichens. We quantified the percentage of standing dead canopy trees across elevational gradients and examined relationships with stand characteristics in 120 plots along five vertical transects between 1650 and 2050 m. We found that an average of 31.1% of canopy trees were standing dead, with significantly higher rates (41.8%) below 1800 m than above 1900 m (11.5%). Subalpine fir ( Abies lasiocarpa) had a higher percentage of standing dead trees (34.7%) than Engelmann spruce ( Picea engelmannii, 15.5%). Upper elevation forests were significantly younger, consistent with post-Little Ice Age establishment. These findings suggest a forest transition process (forest juvenilization) that may initially increase DSC winter forage availability due to higher lichen loadings on standing dead trees. Looking forward, we project a long-term reduction in winter forage as old-growth structure is lost. Our study establishes baseline data for long-term monitoring and highlights the need for further research on the cascading effects of climate-induced forest changes on old-growth-dependent species like DSC.